1. Field of the Invention
The present invention relates to an automatic transfer apparatus for use in a forging press which picks up or clamps a work and transfers it according to a sequential order of the press working cycle.
2. Prior Arts
A typical transfer mechanism has been heretofore known and put into practical use, in which two beam drivers are provided respectively on the left and right sides of a forging press, and three-directional motions, i.e., vertical motion (lift), advance and return (feed), and opening-and-closing motion (clamp) are combined and applied to two beams disposed for connecting horizontally the two beam drivers and putting them between an upper and lower mold, whereby a work clamped between clamping fingers attached inwardly of both beams are transferred and placed at a required place.
It is necessary for the mentioned beam drivers to repeat the above three motions exactly in sequential order so as to be in synchronous with the working operations of the press and, therefore, a transmission mechanism formed in association with control equipment, a tooth gear, a rack, a connecting rod, etc. for receiving rotation of a crankshaft of the press main body is used for conversion to motion of the beams.
A problem, however, exists in that since the association among disc cams, gears, racks, etc. is fixed in such a mechanism, the stroke, timing and speed of the mechanism are quite limited to values within a certain narrow range, and it is not allowed to change the values appropriately according to the size, kind, etc. of the work, resulting in several restrictions or disadvantages in the practical use of the mechanism except large size automatic forging presses with less variation in the work to be processed.
That is, in the widely used transfer type forging press, the work to be processed is thereby of many kinds while the respective amount to be processed is rather small. Accordingly, for performing necessary movements of the beams by means of such a fixed type transfer machine, the arrangement of molds is changed or the fingers mounted on the beams are replaced to overcome the above problem. Such a change or replacement, however, brings about another problem of a decrease in productivity and an increase in complexty of maintenance. A further problem exists in that because of the complicated mechanism combination using a large number of components of high rigidity, the beam drivers are obliged to be large-sized respectively occupying a large space on both the left and right sides of the forging press.
To overcome the above problems, several attempts have been proposed so far, as disclosed in FIGS. 10 and 11 transcripted from Japanese Laid-Open Patent Publication No. 63-215330.
Referring to FIG. 10, servo assistors 101, 102, 103, 104, 105 of the electrical hydraulic type are disposed respectively on three shafts for driving the beams, and thus the three output shafts operated hydraulically by the servo assistors form respectively control shafts 108, 109, 110 for vertical, lateral and opening-and-closing motions of the transfer beams 106, 107. Referring now to FIG. 11, in the servo assistor of the electrical hydraulic type, a driving force is applied from a step motor 111 to a piston cylinder 113 through a control valve 112, and a piston 114 has a piston rod 116 provided with teeth 115 which cooperates with a pinion 117 for feedback of the actual value. Thus, piston rod 116 being an output shaft performs also as a control shaft for driving the transfer beams among three axes. When driving the motor 111, the control valve 112 is displaced with respect to a fixed spindle 119 of the pinion 117 by means of the lateral beam 118, whereby valves 120A, 120B are open to connect cylinder chambers 121A, 121B to the pressure feeder and tank, thus the piston 114 being moved by pressure differential. In effect, the piston rod being an output shaft and also a control shaft acts directly on a mechanical section associated with it through the mechanism control valves for setting mechanical target values, serving as a rack and as a servo assisting section, and as a pinion mechanism.
It is certain that the prior art shown in FIGS. 10 and 11 improves, to a certain extent, transfer motions, and achieves variation in momentum, variation in the relation between one motion axis and the other, and variation in velocity of individual motion axes corresponding to the size of the work or working ratio.
As shown in FIG. 10, however, in the mechanism of this prior art, the control shafts 108, 109 of the servo assistors 101 and 102 perform a vertical linear motion or vertical movement (lift) only, but as for the advance and return (feed) which needs the longest stroke, the linear motion of the control shaft 110 in the servo assistor 103 is converted to rotational motion on the pin 122, which serves as a fulcrum, which motion is transmitted to the transfer beams 106, 107, and those beams turn tracing a locus not horizontally linear but of a large circular arc with respect to the lower mold. That is, not only the horizontal distance but also the vertical distance is involved in the motion of the beams and, as a result, synchronous motion and positional relation in the molds are complicated due to such involvement of other factors. The influence of such a complication is more serious when the feed distance is larger.
Moreover, the control shaft is driven by opening and closing the valve 112, and this movement is directly transmitted to respective mechanical sections through mechanical functions of the rack and pinion, and mechanism for setting target values is mechanically performed. As a result, starting and stopping of the control shaft are performed instantaneously only by mechanical engagement and disengagement of related members. As is well known, if a driving force is repeatedly applied to a shaft in a continuous and regular manner and suddenly stopped at a required position by braking means such as a rack, a considerably large impact force will act on the shaft due to inertial, eventually resulting in accumulation of metal fatigue on the shaft. To prevent such a problem, a large safety factor is estimated for the shaft. However, for the purpose of associating many kinds of motions requiring complicated interlock of the shaft, a driving system as a whole is obliged to be large-sized and heavy-weighted. Furthermore, in the mechanism according to this prior art, many hydraulic mechanisms and pipings therefor are complicatedly incorporated and, accordingly, maintenance under unavoidable operating conditions such as vibration is very troublesome, and perfect maintenance actually difficult to achieve.